The present invention relates generally to vapor recovery systems associated with the fueling of vehicles. More particularly, the present invention relates to a modification made to an assist type of vapor recovery system to improve the performance and compatibility of the system when it is used for refueling vehicles that have on board refueling vapor recovery (ORVR) systems.
In fuel dispensing systems, such as those used for delivering gasoline to the fuel tank of a vehicle, environmental protection laws require that vapors emitted from the tank during the fuel dispensing process be recovered. Fuel is customarily delivered through a nozzle via a fuel hose and vapors are recovered from the nozzle via a vapor hose that conveys the vapors to the storage tank from whence the fuel came. In what is referred to as a balanced system, the vapors are forced through the vapor hose by the positive pressure created in the vehicle tank as the fuel enters it. In other systems, referred to as assist type systems, the vapor is pumped from the vehicle tank and forced into the storage tank by a vapor recovery system connected to the vapor hose. Currently, many fuel dispensing pumps at service stations are equipped with vacuum assisted vapor recovery systems that collect fuel vapor vented from the fuel tank filler pipe during the refueling operation and transfer the vapor to the fuel storage tank.
Onboard, or vehicle carried, fuel vapor recovery and storage systems (commonly referred to as onboard refueling vapor recovery (ORVR) systems) have been developed wherein the ullage or headspace in the vehicle fuel tank is vented through a charcoal-filled canister so that the vapor is absorbed by the charcoal. Subsequently, the fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel and air mixture. The fuel tank headspace must be vented to enable fuel to be withdrawn from the tank during vehicle operation. In typical ORVR systems, a canister outlet is connected to the intake manifold of the vehicle engine through a normally closed purge valve. The canister is intermittently subjected to the intake manifold vacuum by opening and closing the purge valve between the canister and intake manifold. A computer which monitors various vehicle operating conditions, controls the opening and closing of the purge valve to assure that the fuel mixture established by the fuel injection system is not overly enriched by the addition of fuel vapor from the canister to the mixture.
Fuel dispensing systems at service stations having vacuum assisted vapor recovery systems that are unable to detect ORVR systems waste energy, increase wear and tear, ingest excessive air into storage tanks and cause excessive pressure buildup in the piping and storage tanks due to the expanded volume of hydrocarbon saturated air. Refueling of ORVR equipped vehicles using such fuel dispensing systems can be deleterious for both the vapor recovery efficiency of the vapor recovery system and the durability of some of the system components. The refueling of an ORVR equipped vehicle deprives the vapor recovery system of gasoline vapors intended to be returned to the storage tank, typically located underground. Since gasoline vapor is not available in the required quantities, the vapor pump of an assist-type system will pump air back into the storage tank. The air pumped back into the storage tank vaporizes liquid fuel in the storage tank resulting in pressurizing the ullage space of the storage tank so that fuel vapors are then vented to the atmosphere as polluting emissions.
The balance type of vapor recovery system is one of the known types of vapor recovery systems that attempts to avoid these problems. As described above, balanced systems do not use vapor pumps, but simply allow the free exchange of vapor between gasoline tanks of vehicles being refueled and storage tanks from which gasoline is being pumped. Since air is not forced into the storage tank when a fuel dispensing system having a balanced vapor recovery system is used to refuel an ORVR equipped vehicle, the vapor growth problem is avoided and, in fact, the storage tank pressures are typically reduced by the removal of liquid and possibly vapor. The reduction in vapor flow rate when refueling an ORVR vehicle is about 100% (i.e., no vapor or air flow to the storage tank).
One known type of assist vapor recovery system attempts to avoid the storage tank pressurization problem by sensing the presence of ORVR equipped vehicles during refueling and using this information to turn off the vapor pump during the refueling of ORVR equipped vehicles. The system's ability to recognize a vehicle's ORVR system and adjust the fuel dispenser's vapor recovery system accordingly, eliminates problems associated with redundant operation of two vapor recovery systems, i.e., the dispenser's assist type vapor recovery system and the vehicle's ORVR system, for one fueling operation. Examples of this type of system are disclosed in U.S. Pat. Nos. 5,782,275 and 5,992,395, issued to Gilbarco and hereby incorporated by reference. The reduction in vapor or air flow rate during refueling of an ORVR equipped vehicle will be 100% if the vapor pump is turned off; however, some initial run time is required to sense the ORVR system and to turn the vapor pump off. The particular system of the '275 patent utilizes a hydrocarbon sensor to determine if an ORVR fueling event is occurring and the particular system of the '395 patent utilizes a pressure sensor to determine if an ORVR fueling event is occurring. If an ORVR system is detected, the sensor generates a signal that is used to turn the vapor pump off.
Another example of an assist vapor recovery system is described in U.S. Pat. No. 6,095,204, issued to Healy and hereby incorporated by reference. The '204 patent claims a fuel dispenser configured to deliver fuel to a fuel tank of a vehicle including a vapor recovery system having a vapor recovery path for removing fuel vapor during a fueling operation. A vapor controller is also claimed with a pressure sensor operatively associated with the fuel dispenser for sensing an increase in vacuum in the vapor recovery system associated with the vehicle working in opposition to the vapor recovery system for the fuel dispenser with the pressure sensor providing a pressure signal to a vapor recovery controller. A vacuum relief valve setting, in combination with a selected vacuum regulation setting for a chamber of the vapor flow control, produces an air return rate at 75% of the liquid gasoline delivery rate. In this manner, the volume of pure air drawn into the nozzle will only result in liquid gasoline evaporation underground sufficient to bring the total final volume back to a level equal to the liquid volume dispensed. Therefore vent emissions are avoided and vapor recovery system efficiency is maintained.
Another type of known assist vapor recovery system utilizes a vapor flow restrictor built into the nozzle of a fuel dispenser to decrease the vapor flow back to the storage tank during an ORVR refueling event. The nozzle for such a system utilizes a flexible boot to engage the filler neck of a vehicle, but unlike a balance system, an air-tight seal is prevented. If an air-tight seal were present when a vapor pump is being used in conjunction with an ORVR vehicle, relatively high vacuum levels develop within the vapor space of the nozzle. These abnormally high vacuum levels cause abnormal operation of the automatic shut-off mechanism in the nozzle. The nozzle for such a system utilizes either a check valve or holes in the boot itself to limit the amount of vacuum to which the nozzle is exposed. Such vacuum relief measures allow the vacuum level to increase to a detectable level within the nozzle and the elevated vacuum level is used to operate a flow restrictor in the vapor flow path. The exact reduction in vapor (air) flow rate during an ORVR refueling with such a system is from 25% to 78% depending on the exact configuration and fueling flow rate.
Another type of assist system is described in U.S. patent application Ser. No. 10/820,288 filed Apr. 8, 2004, claiming priority to U.S. Provisional Patent Application Ser. No. 60/461,097 filed Apr. 8, 2003, entitled ORVR compatible vacuum assist fuel dispensers and assigned to the assignee of the present application. That system utilizes an assist-type of nozzle and a balance-type flexible boot to seal against the filler neck of the vehicle being refueled. This arrangement results in relatively high vacuum levels in the nozzle vapor space. To accommodate those vacuum levels, the shut-off mechanism is modified. Since the nozzle boot is sealed against the vehicle's filler neck, the vapor recovery system will not ingest appreciable air into the storage tank. However, the vapor flow rate will not be reduced completely by 100% as with a balance system because the vapor pump will be capable of pumping some vapor from the vehicle's fuel tank. The reduction in vapor flow rate is typically about 90% with such a system.
The above-described assist vapor recovery system effectively blocks the inlet or nozzle end of the vapor hose resulting in relatively high vacuum levels in the vapor hose itself. The system described in the '204 patent does so similarly, but to a lesser degree. The vacuum levels in the vapor hose during refueling of an ORVR vehicle will be about ten times higher than the vacuum levels in the vapor hose when refueling a vehicle that is not equipped with an ORVR system. In addition, elevated vacuum levels will be present in the entire length of the vapor hose due to the drastically reduced vapor flow rate. The exterior of the vapor hose is also subjected to the fluid pressure since typically the fluid carrying hose surrounds it in a coaxial arrangement. The exterior pressure combined with the elevated interior vacuum levels presents a condition that promotes the collapse of the vapor hose tubing.
Moreover, the current trends in the industry are to increase the amount of ethanol used in gasoline fuel blends which deteriorates the mechanical properties of the material used in the vapor hose tubing. These factors, in combination with market movements toward single hose dispensers which increases the flexing cycle on the vapor hose tubing, can result in the collapse and/or failure of the vapor hose tubing. Such problems could become systemic and present a significant issue that must be addressed.